ImageSource and ImageSourceServices

[mattleibow]

Description of Change

This PR is trying to handle the case of loading some native "image" using the ImageSource. Right now, this PR only contains Android.

Initially, I tried returning the Drawable directly from the service, but this meant that there was no way to immediately release/dispose/free the bitmap. The GC would eventually get it - maybe. However, we can't rely on the GC as native bitmaps do not put enough pressure on the GC as well as sometimes we want to release them faster.

My solution here is to return a "result" object that contains both the actual drawable as well as some release logic. This logic is very abstract and is just an IDisposable. The actual logic for this dispose is not disposing the drawable directly because this is not up to us. Rather, it wraps the logic needed to reverse the request and comes from the service that created the result.

An example would be Glide that internally caches the bitmap and we have to indicate we are done with it:

• Create: target = Glide.With(context)...Submit()
• Dispose: Glide.With(context).Clear(target)

This logic is generic enough that it can work with any type of result since the service that caches the drawable is responsible for releasing it too.

class FileImageSource : ImageSource
{
    public string File { get; set; }
}

class Image : View
{
    public ImageSource Source { get; set; }
}

Android:

class GlideResult : IImageSourceServiceResult<Drawable>, IDrawable
{
    public GlideResult(Drawable drawable, Action dispose)
    {
        Value = drawable;
        _dispose = dispose;
    }

    // this is the actual drawable to display
    public Drawable Value { get; }

    // this is a way in which to release the image
    public void Dispose() => _dispose?.Invoke();
}

class FileImageSourceService
{
    public async Task<IImageSourceServiceResult<Drawable>?> GetDrawableAsync(IFileImageSource imageSource, Context context) 
    {
        var target = Glide
            .With(context)
            .Load(imageSource.File)
            .Submit();

        var drawable = target.GetAsync();

        return GlideResult(
            drawable: drawable,
            dispose: () => Glide.With(context).Clear(target));
    }
}

Usage

class ImageHandler : ViewHandler
{
    GlideResult _lastSource;

    public static void MapSource(ImageHandler handler, IImage image)
    {
        // clear out the old image
        handler.NativeView.SetImageDrawable(null);
        handler._lastSource?.Dispose();

        if (image.Source == null)
            return;

        // get the new one
        var result = await imageSourceService.GetDrawableAsync(image.Source);
        handler._lastSource = result;
        handler.NativeView.SetImageDrawable(result.Value);
    }
}

TODO

• Animated GIF support on iOS: [Bug] Animated GIF files do not play on iOS/macOS #866
• FontImageSource on Windows has a bad resolution: <Image> does not respect the DPI in a CanvasImageSource microsoft/Win2D#824
• Fix issue with StorageFile in background thread: 0x8001010E (RPC_E_WRONG_THREAD) on Windows API call microsoft/CsWinRT#612
• Make old imagesource handlers handlers use new services: [Bug] Missing integration between old ImageSourceHandlers and new ImageSourceServices #867

[PureWeen]

Is there a general place this value can get stored? Or maybe an extension method we can make that represents this flow of operations

var token = NAtiveView.WatchForRasterChanges(() => callback);
NativView.StopWatchingForRasterChanges(token)

[mattleibow]

Yes. #887

This also happens on iOS. I assume Android does not change, but I am probably wrong. I also need to add that. Maybe.

[PureWeen]

#882

[PureWeen]

#883

[PureWeen]

Cool!
Looks good

I think we should add back the preserve for now because the CG needs it for AppCenter tests and it's confusing when that one crashes for that reason

[jsuarezruiz]

Could we have also some image benckmark in the Benchmarks project?. I am thinking mostly in images from Url where things like Glide will have a huge impact but also, the metrics could help us to progress and improve (for example, with changes related with cache).

(Not necessary in this PR)

[jsuarezruiz]

Agree, could fix several issues like xamarin/Xamarin.Forms#13629

[jsuarezruiz]

Probably in the future will have more sense in something like ApplicationHandler if exists but looks good to me.

[jsuarezruiz]

Out of curiosity, what is the size of Glide library?

[mattleibow]

1.8MB when the aar is embedded in the dll from the nugets. About 767KB of jar files. The linker/proguard should help a bit on this.

[jsuarezruiz]

Should we include CancellationToken here to allow cancel the loading operation?

[mattleibow]

This happens inside:

var token = handler._sourceManager.BeginLoad();

The existing token is cancelled and starts a new source and returns the token to be used with UpdateSourceAsync

[jsuarezruiz]

❤️

[Pinox]

Hi @mattleibow ,

I am currently using FFImageloading with Xamarin Forms. I am checking out my dependencies in my current project for upgrade to MAUI. FFImageloading is a concern as I used it for fast image rendering on Android & iOS. As the Glide functionality is now integrated into MAUI for Android I have one less concern ;))

Looking at the FFImageloading repo it does not seem to be supported anymore by the authors. In nuget the latest download stats on the latest version is around 4.2 million downloads

https://www.nuget.org/packages/Xamarin.FFImageLoading/

So alot of developers are going to trip on this library. One of the other features I used FFImageloading for was Retry Count + Retry Delay for redundancy reasons.

This is a must on mobile devices that connects to unstable / intermittent internet connections to prevent for eg a listview from skipping images and displaying nothing.

Any chance that the MAUI team can support Retry Count & Retry Delay within MAUI ?

[pictos]

@Pinox can you open an issue proposing this feature?